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MECA Electronics

Capacitor Dielectric Properties

The question arises all the time concerning which capacitor type to use for a particular application. This table provides a guideline for starters, but is in no way exhaustive. (DA = dielectric absorption)

The unofficial temperature coefficient designations for the capacitors are as follows: The temperature coefficient is given as "P" for positive, "N" for negative, followed by a 3-digit value of the temperature coefficient in ppm/°C. For example "N220", is -200 ppm/°C, and "P100" is +100 ppm/°C. The one exception in this system is "NPO" where an "O" instead of "0" is used, but quite a number of people use "NP0." In any event "NPO" means stable with temperature.

Dielectric Type DA Advantages Disadvantages Uses
NPO Ceramic
(COG)		 <0.1% Tight tolerance
High Q factor, low K
Small case size
Inexpensive
Good stability
Wide range of values
Low inductance		 DA generally low, but may not be specified
Limited to small values (10 nF)		 Low loss, timing and tuning applications
Monolithic
Ceramic
(High K)		 >0.2% Low inductance
Wide range of values		 Poor stability
Poor DA
High voltage coefficient		  
X7R  (BX)
(Barium Titanate)		   Inexpensive
Low DA available
Wide range of values
Smaller case size		 Damaged by temperature
    >+85° C
Loose tolerances
High inductance		 Bypassing, coupling, and frequency discrimination circuits
Z5U & Y5V   Smallest case size
Very large values		 Damaged by voltages
    >25 WVDC
Very loose tolerances		 Bypassing and coupling
Polystyrene 0.001%
to 0.02%		 Inexpensive
Low DA available
Wide range of values
Good stability		 Damaged by temperature
    >+85° C
Large case size
High inductance		 Timers and filters
Polypropylene 0.001%
to 0.02%		 Inexpensive
Low DA available
High dielectric strength
Wide range of values
Negative TC		 Damaged by temperature
    >+105° C
Large case size
High inductance		 Stable oscillators and filters, sample and hold circuits and pulse handling circuits
Teflon 0.003%
to 0.02%		 Low DA available
Excellent stability
Operational >+125° C
Wide range of values		 Relatively expensive
Large size
High inductance		 Timing and pulse shaping circuits
MOS 0.01% Good DA
Small
Operational above +125° C
Low inductance		 Limited availability
Available only in small capacitance values		  
Polycarbonate 0.1% Good long-term stability
Low cost
Wide temperature range		 Large size
DA limits to 8-bit applications
High inductance		 Timers, filters and applications in high ambient temperature
Polyester 0.3%
to 0.5%		 Moderate stability
Low cost
Wide temperature range
Low inductance (stacked film)
Self-healing		 Large size
DA limits to 8-bit applications
High inductance		 Bypassing and coupling
Mica >0.003% Low loss at HF
Low inductance
Very stable
Available in 1% values or better		 Quite large
Low values (<10 nF)
Expensive		  
Aluminum Electrolytic High Large values
High currents
High voltages
Small size		 High leakage
Usually polarized
Poor stability
Poor accuracy
Inductive		  
Tantalum Electrolytic High Small size
Large values
Medium inductance
High melting point
High dielectric strength
Good ductility		 Quite high leakage
Usually polarized
Expensive
Poor stability
Poor accuracy		  

 

Related Pages on RF Cafe
- Capacitors & Capacitance Calculations
- Capacitor Color Codes
- Capacitance Conversions
- Capacitor Dielectrics
- Standard Capacitor Values
- Capacitor Vendors
- The Noble Art of De-Coupling

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